1. Field of the Invention
The subject invention relates to a vehicle drive system, and more particularly, to a highly efficient drive system for a hybrid electric automobile which employs both a combustion engine and an electric motor to power the vehicle.
2. Description of the Related Art
For nearly a century, automobiles have been powered by internal combustion engines, which by the very nature of their fuel burning process, emit harmful waste products into the environment. Recently, vehicles that are powered solely by electric motors have been introduced in an attempt to minimize the amount of hazardous waste being admitted to the air. Electric vehicles are limited in their range and applicability however, since they possess large storage batteries that must be recharged over an extended period of time.
Automobiles utilizing both an internal combustion engine and an electric motor for power are also known in the art, and are commonly referred to as hybrid powered vehicles. These vehicles are designed to minimize harmful effluents and maximize the beneficial aspects of gas engines and electric motors. Early examples of hybrid electric vehicles are disclosed in U.S. Pat. No. 2,571,284 to P. T. Nims; U.S. Pat. No. 3,305,965 to R. Roth; and U.S. Patent No. 3,791,473 to Rosen. In general, there are two types of hybrid electric vehicle drive systems. A parallel drive system in which the internal combustion engine and the electric motor work in conjunction to power the drive wheels of the vehicle, and a series drive system wherein the internal combustion engine powers a generator for the electric motor and the electric motor delivers power to the drive wheels of the vehicle.
An example of a hybrid powered vehicle which employs a modified parallel drive system is disclosed in U.S. Pat. No. 4,042,056 to Horwinski. The modified drive system includes an internal combustion engine that delivers power to a front drive shaft of the vehicle and an electric motor that delivers power to a rear drive shaft of the vehicle through an automatic transmission. In operation, the electric motor and the automatic transmission are used to accelerate the vehicle to highway cruising speed. When or shortly before cruising speed is attained, the internal combustion engine is started and a magnetic clutch connects the engine to the front drive shaft. At the same time, the internal combustion engine can be employed to drive a generator that charges the batteries which deliver power to the electric motor.
Another hybrid electric vehicle which employs an internal combustion engine to drive the front wheels of the vehicle and an electric motor to drive the rear wheels of the vehicle, and which provides a mechanism for selecting between the two is disclosed in U.S. Pat. No. 4,351,045 to Fields et al. Other hybrid vehicle drive systems are disclosed in U.S. Pat. No. 3,732,751 to Berman et at.; U.S. Pat. No. 3,888,352 to Reinbeck; U.S. Pat. No. 4,423,794 to Beck; and U.S. Pat. No. 4,242,922 to Baudoin.
To date, there has not been a hybrid electric vehicle with a drive system delivering power to one set of drive wheels, that can operate in both a parallel configuration and a series configuration depending upon the driving conditions encountered by the driver. Such a system would promote the optimum utilization and distribution of energy in a hybrid electric vehicle, while maximizing efficiency and minimizing harmful pollutants.